"I have reopened the hearing because I believe that anyone who comes forward with allegations of sexual assault has a right to be heard, and because it is the Committee's responsibility to fully evaluate the fitness of a nominee to the Supreme Court," the Iowa Republican wrote.

The Senate, the committee chairman notes, "and only the Senate", is tasked with vetting a president's Supreme Court nominee.

"The FBI does not make a credibility assessment of any information it receives with respect to a nominee.

"Nor is it tasked with investigating a matter simply because the Committee deems it important."

Image copyrightReutersImage caption
Prof Ford says Brett Kavanaugh pinned her to a bed and tried to take off her clothes

Back in 1991, however, the FBI did investigate sexual harassment claims against then-Supreme Court nominee Clarence Thomas.

The White House under President George H W Bush ordered that inquiry. It took three days, CNN notes, and the claims by Anita Hill were dismissed as unfounded.

Judge Thomas was narrowly confirmed and he remains a Supreme Court justice.

Mr Grassley's letter states that Prof Ford has until Friday morning to provide the committee with her prepared testimony and biography if she plans to testify next Monday.

He said he was "disturbed" to hear that she had been facing threats and harassment, but urged her to speak before the committee.

"You have stated repeatedly that Dr Ford wants to tell her story. I sincerely hope that Dr Ford will accept my invitation to do so, either privately or publicly, on Monday."

Image copyrightGetty ImagesImage caption
Judge Kavanaugh has been meeting with officials at the White House this week

Prof Ford has accused him of drunkenly trying to remove her clothing at a house party in a Washington DC suburb in 1982 when they were both teenagers.

She says he pinned her to a bed and clamped his hand over her mouth when she tried to scream.

Anita Hill - whose allegation against Clarence Thomas has drawn endless parallels with the Ford-Kavanaugh controversy - says the accuser must not be hurried.

"Do not rush these hearings," she wrote in an opinion piece for the New York Times.

"Doing so would not only signal that sexual assault accusations are not important."

What are Trump and other Republicans saying?

On Wednesday, President Donald Trump continued to support his nominee, telling reporters outside the White House: "He is such an outstanding man, [it is] very hard for me to imagine anything happened."

"I want to see what she [Prof Ford] has to say but I want to give it all the time they need," the Republican president said. "If she shows up that would be wonderful."

Republican Senator Lindsey Graham tweeted on Wednesday that it was "imperative" to move forward on the Kavanaugh vote.

Requiring an FBI investigation of a 36 year old allegation (without specific references to time or location) before Professor Ford will appear before the Judiciary Committee is not about finding the truth, but delaying the process till after the midterm elections.

I hope that Dr. Ford will reconsider and testify before the Senate Judiciary Committee on Monday. It is my understanding that the Committee has offered to hold either a public or a private session, whichever would make her more comfortable.

When Dr. Ford came forward, I said that her voice should be heard and asked the Judiciary Committee to delay its vote on Judge Kavanaugh. It did so. I now implore Dr. Ford to accept the invitation for Monday, in a public or private setting. The committee should hear her voice.

Meanwhile, Democratic Senator Claire McCaskill - who is facing a tough re-election fight in Missouri - said she will "vote no on Judge Kavanaugh".

"My decision is not based on those allegations but rather on his position on several key issues, most importantly the avalanche of dark, anonymous money that is crushing our democracy," she said in a statement.